Oxidation of methacrolein or acrolein to the corresponding acid and peroxide in the presence of iodine



United States Patent M 3,114,769 OXIDATEUN 0F METHACRULEIN 0R ACROLETN T0 TIE CQRRESPGNDHNG ACID AND PER- OXTDE IN THE PRESENCE OF IODWE Bruno .l. Barone, Levittown, Pa, and Wiliiarn F. Brill,

Skillman, I l-1L, assignors to Petro-Tex Chemical Corporation, Houston, Tex., a corporation of Delaware No Drawing. Filed Jan. 11, 1961, Ser. No. 81,934 3 Claims. (Cl. 260-530) This invention relates to an improved process for the production of polymerizable aliphatic monoethylenically unsaturated acids, such as methacrylic, from the corresponding unsaturated aldehydes by oxidation in liquid phase with molecular oxygen.

The production of unsaturated aliphatic acids by the oxidation of the unsaturated aldehydes in liquid phase has heretofore been difficult because of the ease with which the unsaturated acids polymerize once they are formed. The prior art has attempted to prevent polymer formation by several procedures, one such attempt has been to carry out the oxidation in the presence of relatively large quantities of diluent for the reaction mixture. However, even with the use of diluents large amounts of polymer were still produced.

The use of conventional polymerization inhibitors such as hydroquinone or pyrogallol would at first seem to be a possible method, but unfortunately, they are also wellknown antioxidants and therefore inhibit the reaction.

In accordance with this invention, a process has been found whereby unsaturated aliphatic aldehydes may be oxidized with molecular oxygen in the liquid phase to high yields of the corresponding unsaturated acid with only relatively small quantities of polymer being formed. The process comprises carrying out the oxidation in liquid phase at low temperatures and in the presence of a small quantity of iodine.

Useful aldheydes as starting materials are compounds of the general formula wherein R is either hydrogen or a lower alkyl group. The alkyl group may contain, for example, from one to six carbon atoms. The preferred aldehydes are methacrolein and acrolein. Mixtures of aldehydes may be used. The corresponding acids of the formula are produced.

The iodine may be added to the reaction mixture as either free iodine or as a compound which will generate free iodine under the conditions of reaction. The amount of iodine should be from about .001 to about 2.0% by weight of the total reaction mass. Higher concentrations of iodine may be used but at higher concentrations the rate of oxidation is undesirably low. The preferred concentration of iodine is from about .02 to 1.0 weight percent. When methacrolein is employed as the aldehyde feed the iodine may suitably be present in an amount of about .02 to 1.0 weight percent of iodine based on the methacrolein.

The oxidation is preferably carried out on the aldehyde in bulk, that is, with essentially no diluent or solvent present. If any solvent or diluent is used, it should be inert to the oxidation under the defined reaction conditions. The solvents or diluents, if any, which may be used include saturated acids such as formic acid and acetic acid; esters such as methyl acetate and ethyl ace- 3,114,769 Patented Dec. 1'7, 1963 tate; aliphatic or aromatic halides, such as carbon tetrachloride, and chlorobenzene; the saturated hydrocarbons such as heptane and nonane; petroleum hydrocarbon fractions such as petroleum naphtha or gasoline; and aromatic hydrocarbons such as benzene or xylene. The reaction solution will preferably contain at least weight percent of aldehyde and more preferably will contain at least weight percent of the aldehyde. The best results were obtained by oxidizing the aldehyde in bulk.

While the reaction may be conducted without the addition of a catalyst, the rate of reaction may be increased by the use of light or by the use of an oxidation catalyst. These catalysts may be finely divided polyvalent metals which have an atomic number of about 22 to about 82. Compounds of metals are also useful, including the ox ides, and the inorganic or organic salts. Examples of the types of catalyst that may be employed are the metals such as cobalt, vanadium, cerium, copper, manganese, silver and uranium and the combination of these metals with organic, nitric or phosphoric acids. Specific examples of useful compounds are cobaltic acetylacetonate, cobalt naphthenate, cobaltous acetate, mangnesium oxide, manganese acetate, barium acetate and barium butyrate. The preferred catalysts are cobalt, manganese and nickel salts, including cobaltic acetylacetonate, cobalt naphthenate, cobaltous acetate, manganese oleate and nickel oleate.

Oxygen may be added either as pure oxygen or as oxygen diluted with inert diluents such as nitrogen or helium. Either air or air enriched with oxygen may be used under certain conditions. Preferably the gaseous mixture should contain at least 70 mols percent of molecular oxygen and more desirably the gas should contain at least mol percent molecular oxygen. Best results were obtained when essentially no diluent was used with the oxygen. The oxygen may be contacted with the reaction mixture by admixture with the aldehyde in any convenient manner. The oxygen may simply be bubbled through the reaction mass or equipment particularly adapted to gas-liquid mixing may be used. Mixers such as bubble towers, turbo-absorbers, jets, scrubbers, and devices for re-circulating through towers or nozzles are useful. Generally, the reaction mass should be agitated by mechanical stirrers or other means. The oxida tion may be conducted either batch-Wise or continuously. The gas and liquid flow may be in the same direction or counter-current. The reaction may be conducted at any temperature from about -l0 C. to 50 C., but better results have been observed when temperatures of about 0 C. to 35 C. are used. The preferred range is from about 0 C. to 15 C. Temperatures in excess of 50 C. should be avoided as lower yields of the unsaturated acid are obtained at higher temperatures.

The oxidations are conducted in the liquid phase at either subatmospheric, atmospheric or superatmospheric pressure. When more volatile aldehydes are employed as the feed, it may be desirable to use pressure higher than atmospheric to avoid loss of aldehyde through vaporization. Atmospheric pressure may be used, although higher conversions sometimes are achieved at higher pressures. Pressures from about atmospheric to 50 p.s.i.g. are preferred.

The product of the oxidation contains a mixture of the unsaturated acid, acid peroxides, aldehyde peroxides, and unreacted aldehyde, and may contain relatively minor amounts of other reaction products. For example, when methacrolein is used as the feed, the product would include both some methacrylic acid and methacrolein peroxide. The unsaturated acid may be recovered by conventional processes as by distillation or solvent extraction and by decomposition of the peroxides with heat. If distillation is employed, the distillation should preferably be conducted under subatmospheric conditions to avoid polymerization. Distillation is dangerous unless the peroxides are decomposed first, or a high boiling diluent is added to dilute the peroxides.

The unsaturated acids produced by this invention have numerous well known commercial applications, for example, as monomers in the production of synthetic resins.

The following examples are by way of illustration only, and are not to be considered as limiting the invention. All percentages are by weight unless otherwise stated.

Example 1 200 ml. of freshly distilled methacrolein and 0.1 Wt. percent of iodine is charged to a 500 ml. three-necked reaction flask. The flask is fitted with a gas inlet tube, reflux condenser, thermometer, high speed magnetic stirrer and stirring bar. Agitation is begun and the temperature maintained at C. by circulating water from a constant temperature bath through the water jacket of the reactor. Oxygen, measured by a wet test meter in the inlet system, is admitted to the reaction so as to maintain an offgas flow of 10 to ml. per minute. The off gas passes through a Dry Ice trap to collect all condensables present and then flows through an ascarite trap for removal of carbon dioxide, a second wet test meter and finally a rotometer for regulation of off gas flow. The dark yellow brown color imparted to the solution by the iodine gradually lightens in intensity during an induction period of about 140 minutes. The oxidation proceeds smoothly and is terminated after approximately 0.25 mole of oxygen has been absorbed per mole of aldehyde charged. This represents 50% of the theoretical oxygen. This takes hours and gives an aldehyde conversion of 32% as shown by gas chromatography. The product contains 1.34 moles/liter of peroxide by iodometric titration (which is a 76.4% yield on methacrolein consumed) and free'methacrylic acid.

The effect of the iodine in retarding polymer formation was shown by flash distillation of a 10 ml. sample of the oxidate at 5 mm. of mercury over a bed of copper pellets maintained at a temperature of 130 C. 96% of the sample was recovered with only 4% residue. The amount of polymer present in the product was therefore 4% or less.

Example 2 Example 1 was repeated at the same temperature and for the same time with the exception that the iodine was omitted. On flash distillation a 15.3% polymeric residue remained which was about four times the polymer residue of Example 1.

Example 3 The experiment described in Example 1 was repeated at 5 C. A theoretical yield of peroxide of 77.6% was realized, based on aldehyde consumed, at an aldehyde conversion of 22.4%. Very little polymer formed as shown by the high yields of methacrylic acid which could be obtained on treating the product to decompose the peroxides formed during the oxidation as follows:

The methacrylic acid was recovered by feeding the reaction product into a 100 ml. three-neck flask containing m1. of absolute ethyl alcohol and 0.1 g. of para-toluene sulfonic acid and 0.01 g. hydroquinone. The flask was fitted with a micro Vigreaux column, about 8 inches long and 1 inch wide, and a micro distillation head capable of total reflux. A dropping funnel containing 50 ml. of the reaction product was fitted to the other neck. The alcohol was heated to reflux with a flask temperature of 78 C. The reaction product was added dropwise to the refluxing alcohol over a two-hour period. During this addition methacrolein is recovered overhead along with some alcohol. Upon the completion of this addition, the reaction mixture is refluxed for one hour to insure complete peroxide decomposition. The distillation is then continued at atmospheric pressure to recover the alcohol and is completed under reduced pressure, 5 mm. of Hg, to recover the methacrylic acid. The individual fractions obtained were analyzed by gas chromatography. The yields of ester and free methacrylic acid, based on the amount of aldehyde charged which was consumed in the process are 4.97% and 91.6% respectively.

We claim:

1. A process for the preparation of a mixture of methacrylic acid and methcrolein peroxide which comprises passing gaseous, molecular oxygen through liquid methacrolein at a temperature of about 0 C. to 15 C., said methacrolein containing about .02 to 1.0 weight percent of iodine based on the total reaction mass.

2. A process for preparing a mixture of methacrolein peroxide and methacrylic acid which comprises passing gaseous molecular oxygen through liquid methacrolein containing about 0.001 to 2.0 weight percent iodine by weight of the total reaction mass at a temperature of about 0 C. to about 35 C.

3. A process for preparing a mixture selected from the group consisting of a mixture of acrolein peroxide and acrylic acid and a mixture of methacrolein peroxide and methacrylic acid which comprises passing gaseous molecular oxygen through the corresponding aldehyde selected from the group consisting of liquid acrolein and liquid methacrolein respectively, said aldehyde containing about 0.001 to 2.0 weight percent iodine based on the total reaction mass at a temperature of about l0 C. to 50 C.

OTHER REFERENCES Boundy et al.: Styrene, p. 21 (1952). 

1. A PROCESS FOR THE PREPARATION OF A MIXTURE OF METHACRYLIC ACID AND METHCROLEIN PEROXIDE WHICH COMPRISES PASSING GASEOUS, MOLECULAR OXYGEN THROUGH LIQUID METHACROLEIN AT A TEMPERATURE OF ABOUT 0*C. TO 15*C., SAID METHACROLEIN CONTAINING ABOUT .02 TO 1.0 WEIGHT PERCENT OF IODINE BASED ON THE TOTAL REACTION MASS. 